This invention generally relates to a valve for controlling vehicle brake operation. More particularly, this invention relates to a combination valve assembly that operates as a combination inversion and relay or inversion and quick release valve.
Heavy vehicles such as trucks typically include air powered brake systems. To protect against brake failure in the event of a loss of air pressure, emergency brake arrangements include a spring that applies a mechanical braking force to stop the vehicle in the event of a brake system pressure failure. Such arrangements are typically referred to as spring applied, air release brake systems. Such arrangements are well known.
The brake actuators of conventional brake systems typically include a service chamber and a spring chamber. The service chamber is selectively pressurized to apply a braking force at the actuator. The pressure is typically controlled by a manually operated foot brake pedal. The spring chamber houses a spring that is biased to apply a braking force. Air pressure within the spring chamber acts against the bias of the spring to hold off any braking force that would be imposed by the spring. By selectively controlling the pressure within the spring chamber, the emergency brake operation is controlled.
The spring housed within the spring chamber typically also serves as a parking brake. When it is desirable to park a truck and apply the parking brake, the pressure is released from the spring chamber and the spring is free to move into a position to apply the parking brake. This is typically controlled using a manually operated valve mounted on the dash within the vehicle. Such arrangements are well known.
Typical brake systems include an inversion valve within the air conduits for selectively controlling the supply of air pressure to the spring chamber. In addition to the inversion valve, a quick release valve or a relay valve is also used for controlling the supply of air pressure to the spring chambers. Two separate valves each in their own housing are commonly used. The use of two valves introduces complexities and expenses into the braking system. Additional tubing or other connections are required between the multiple valve housings. Additionally, each valve housing contains a number of components, which introduces complexity and expense into the system.
It is desirable to reduce the cost of vehicle braking systems while still providing the function of the emergency and parking brake needed to meet government regulations, for example. Moreover, it is desirable to reduce the complexity of the system, reduce installation labor, reduce the number of components and material required and to facilitate easier maintenance of a vehicle brake system. This invention addresses those needs by providing a unique combination valve arrangement where the functions of an inversion valve and a quick release or a relay valve are incorporated into a single valve assembly having a single housing.
In general terms, this invention is a combination valve that provides the combined features of an inversion valve and a relay valve or an inversion valve and a quick release valve depending on the particular configuration.
In one example, a vehicle brake system designed according to this invention includes at least one brake actuator having a service chamber and an emergency chamber. the service chamber is pressurized to apply a braking force. The emergency chamber is pressurized to hold off a braking element (i.e., a spring) that otherwise provides an emergency braking force. A pressure source provides fluid pressure to the brake actuator to control the application of a braking force. Only one valve couples the brake actuator emergency chamber to the pressure source. The valve has an inlet coupled to the pressure source and an outlet coupled to the emergency chamber. The valve includes a single piston that moves responsive to pressure at the inlet from the first position where pressure is exhausted from the emergency chamber to a second position where the emergency chamber is pressurized.
By controlling the movement of the piston within the valve, the amount of pressure to the emergency chamber is selectively controlled. The valve allows for applying different amounts of braking force using the braking element (i.e., the spring) within the emergency chamber.
In one example, the single valve is a combination inversion and relay valve. In this example, there is an inlet to the valve that is directly coupled to the pressure source. A second inlet is coupled to a dash valve that is controlled by a vehicle operator to release or set a parking brake.
In another example, the valve is a combination quick release and inversion valve. In this example, only one inlet to the valve is coupled to the dash valve control. The other inlet, which was used in the relay valve example, preferably is plugged. Additionally, a separate flow path within the valve housing is opened in the inversion valve example.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiments. The drawings that accompany the detailed description can be briefly described as follows.